A stent is a generally cylindrical prosthesis introduced into a lumen of a body vessel via a catheterization technique. Stents may be self-expanding or balloon expandable. Stents are typically crimped from an initial relatively large (or expanded) diameter to a smaller, crimped diameter prior to advancement to a treatment site in the body. Before crimping, a balloon-expandable stent is typically placed over an expandable balloon on a catheter shaft. In cases where the stent was manufactured in its fully crimped diameter, the stent is often expanded and then crimped on the balloon. A crimping device, or crimper, is used to crimp the stent to its crimped diameter for delivery.
In recent years, a variety of prosthetic valves have been developed wherein a valve structure is mounted on a stent and then delivered to a treatment site via a percutaneous catheterization technique. Prosthetic valves are typically much larger in diameter relative to coronary stents. For example, a typical coronary stent diameter is only 1.5 to 4.0 mm in its expanded size, while a stented prosthetic valve diameter will typically be in the range of about 19 to 29 mm, at least 5 times as large as a coronary stent. In another difference, coronary stents are stand-alone devices while, for prosthetic valves, the stent functions as a scaffold to hold the valve structure. The valve structure is typically made of biological materials such as pericardium valves or harvested valves. For improved function after deployment, it is often desirable to package and store such valves in the open (i.e., expanded) diameter inside a preserving solution up until the time the valve is mounted on a delivery device for implantation. Using this procedure, it may be necessary to crimp the valve in the operation room a few minutes before implantation, therefore precluding pre-crimping by the manufacturer. Thus many crimping devices are now shipped as a disposable accessory along with the valve and delivery system, thus increasing the importance of portability of such crimping devices.
Generally, conventional crimping devices operate by one of two methods. In one method, a stent is driven through a cone-like surface, which compresses the stent to a smaller diameter. For example, a static conical tube can be passed over a stent, thereby reducing its diameter. While this method can be effective for some stents formed from easily deformable materials (e.g., Nitinol), it is less effective for stents formed from more rigid or stiffer materials. Furthermore, even for stents formed from easily deformable materials, the design of the stent can sometimes prohibit the use of a static conical tube for crimping. For example, strut thickness and other design features of the frame can create a high radial force which would prohibit the use of a static conical tube.
The second method uses crimping jaws to create a cylinder-like surface that can change diameter. This method is effective for stents formed of both easily deformable materials as well as less deformable materials. One example of such a crimping device is disclosed in U.S. Pat. No. 7,530,253 (hereafter “the '253 patent”), which is incorporated herein by reference. The device disclosed in the '253 patent uses a spiral track positioned around the jaws to drive the crimping jaws in a radial direction, thus operating in the plane of crimping. The device of the '253 patent, however, has limited portability, due to increases in its size and weight when designed for stents of over 29 mm expanded diameter.
Other conventional devices having crimping jaws use, for example, sloped grooves in the plane of crimping to drive the jaws, or rotational motion within the plane of crimping. Such devices with mechanisms within the plane of motion can disadvantageously be limited in terms of size, weight, crimping strength, mechanical advantage, and control of the crimping process. Additionally, newer medical devices sometimes contain components or features that are not designed to be crimped. Conventional crimping devices cannot accommodate such medical devices, because the crimping devices are simply designed to crimp the entire medical device. There thus remains a need for an improved crimping device that addresses these and other disadvantages in the prior art and that has improved portability and a simplified design.